# Schrödinger's cat

## Thought experiment in quantum mechanics / From Wikipedia, the free encyclopedia

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In quantum mechanics, **Schrödinger's cat** is a thought experiment, sometimes described as a paradox, of quantum superposition. In the thought experiment, a hypothetical cat may be considered simultaneously both alive and dead, while it is unobserved in a closed box, as a result of its fate being linked to a random subatomic event that may or may not occur. This thought experiment was devised by physicist Erwin Schrödinger in 1935^{[1]} in a discussion with Albert Einstein^{[2]} to illustrate what Schrödinger saw as the problems of the Copenhagen interpretation of quantum mechanics.

In Schrödinger's original formulation, a cat, a flask of poison, and a radioactive source are placed in a sealed box. If an internal radiation monitor (e.g. a Geiger counter) detects radioactivity (i.e. a single atom decaying), the flask is shattered, releasing the poison, which kills the cat. The Copenhagen interpretation implies that, after a while, the cat is *simultaneously* alive *and* dead. Yet, when one looks in the box, one sees the cat *either* alive *or* dead, not both alive *and* dead. This poses the question of when exactly quantum superposition ends and reality resolves into one possibility or the other.

Although originally a critique on the Copenhagen interpretation, Schrödinger's seemingly paradoxical thought experiment became part of the foundation of quantum mechanics. The scenario is often featured in theoretical discussions of the interpretations of quantum mechanics, particularly in situations involving the measurement problem. As a result, Schrödinger's cat has had enduring appeal in popular culture. The experiment is not intended to be actually performed on a cat, but rather as an easily understandable illustration of the behavior of atoms. Experiments at the atomic scale have been carried out, showing that very small objects may exist as superpositions; but superposing an object as large as a cat would pose considerable technical difficulties.^{[citation needed]}

Fundamentally, the Schrödinger's cat experiment asks how long quantum superpositions last and when (or *whether*) they collapse. Different interpretations of the mathematics of quantum mechanics have been proposed that give different explanations for this process, but Schrödinger's cat remains an unsolved problem in physics.